The man, fired from the H.R. Nicholson Co. about two months ago, drove to the company's northwest Baltimore headquarters shortly before 8 p.m. Armed with a shotgun, he walked through a door and asked for the evening supervisor, who had been his boss, according to police.
About a dozen employees inside at the time scrambled to safety as the man opened fire on the supervisor.
The gunman then walked outside the building, where he sat with the shotgun in his lap until police arrived. He pointed the gun at the officers, who opened fire, according to AP.
The man underwent surgery at a hospital and his condition was not immediately available.
It was unclear who fired the man from his job, or why he was let go, police said.